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Optimization of microalgal biomass harvesting is essential to produce effective and optimum outcomes that can contribute towards a feasible and economical harvesting technique. Two Chlorella species were used, namely, C. vulgaris and C. sorokiniana UKM3. Two essential factors affecting microalgal biomass harvesting via flocculation, namely, the initial pH of the microalgal broth and flocculant (chitosan) concentration were studied. The optimization process was conducted by using a response surface methodology (RSM) based on the model of face-centered-central composite design (FC-CCD). The potential for biofuel application of the harvested biomass was evaluated based on the production of fatty acid methyl esters (FAMEs) by transesterification. The quadratic models obtained from the RSM significantly fitted the experiment data as the p-values were less than 0.05. The initial pH of the microalgal suspension was found to have a more significant effect on the flocculation process than flocculant concentration. For C. vulgaris, the highest flocculant efficiency of 98.7% was obtained at a chitosan concentration of 0.2 g L−1 and an initial pH of 12.0, whereas for C. sorokiniana UKM3, at 0.15 g L−1 of chitosan and initial pH of 12.0 produced the highest efficiency of 97.1%. The harvested biomass of both species exhibited a high content of palmitic acid (C16:0) with 29.74 wt% and 11.81 wt% of dry biomass for C. vulgaris and C. sorokiniana UKM3, respectively. This study showed that Chlorella species can be harvested efficiently using the flocculation process and manifested an excellent potential for biodiesel production where palmitic acid (C16:0) is one of the main compounds for high-acid oil-biodiesel. [ABSTRACT FROM AUTHOR]

Palm oil mill effluent (POME) is a highly polluted agro-industrial wastewater. The CO2 in industrial flue gas requires treatment before it can be discharged into the environment. Utilizing microalgae as the agent to treat wastewater and industrial flue gas is a waste-to-wealth approach. The resulting biomass can be commercialized in the form of valuable products. Chlorella sp. is a microalgal species that can tolerate the pollutant load and has been proven to be a suitable species for CO2 fixation. In this study, Chlorella sp. was cultivated in POME with the aim of reducing the pollutants in the POME and simultaneously capturing CO2. The optimization of the operational conditions of this microalgae-based treatment system was carried out using the response surface methodology (RSM) face centered-central composite design (FC-CCD). Operational factors include the air concentration of CO2 (10-25% v/v), the inlet gas flow rate of 500-2000 mL min−1, and initial inoculum concentration (10-30% v/v) of Chlorella sp. cultivated in POME. The target deliverables include the maximum amount of CO2 fixed by Chlorella sp. and the total nitrogen (TN) reduction as indicators of pollutant reduction by this treatment system. We found that a limited supply of CO2 caused growth limitation, while excess CO2 resulted in acid production that triggered microalgae growth inhibition. The optimum operational conditions were 10% v/v CO2, 1670 mL min−1 aeration rate, and 24.8% v/v inoculum concentration, predicted to simultaneously fix CO2 at 0.12 g of CO2 L−1 day−1 and reduce 80.9% TN, respectively. [ABSTRACT FROM AUTHOR]